The Delhi government said pollution levels reduced across monitoring stations but the scientific jury is still out. Of course, experts say, fewer cars on the road — New Year also being a restricted holiday — means better news for air quality. However, given the interplay of many factors — and an unusually high daytime temperature — experts said, it’s not so easy to jump to any conclusion on Day One.
Going by data, a dip in particulate matter — PM 10 (particle below 10 micron in diameter) and PM 2.5 (below 2.5 micron and more dangerous given the smaller size) — was seen until the first half of the day in many stations while a combination of weather factors and emissions probably led to a spike in the second half. Particulate matter is one of the ingredients in vehicular exhaust.
Said Gufran Beig, project director of Ministry of Earth Sciences’ air quality division: “Last night was bad for air quality due to a lot of vehicle movement and firecrackers to mark New Year. This combined with a fall in temperature by at least 1.5 degrees Celsius from previous night elevated PM 2.5 level significantly. However as the 1st day of 2016 day began, it took some time to recover from last night’s emissions.”
Accoridng to Beig, the transport sector contributes to 40 per cent of the man-made emissions in Delhi. “Cars contribute to half of this which was further reduced today since an estimated half of them (the even half) were off the road. The net impact in all emissions is around 15 per cent.”
A study of data recorded today showed that beginning 8 am, when the odd-even came into effect, PM 2.5 levels began to go down through the morning until 2 pm, a total fall of 10 per cent over the previous day’s level. But after 2 pm, there was an increase in PM 2.5. “We need to examine this scientifically,” said Beig. “Probably, the day’s high temperature (5 degrees above normal), played a role in this spike.”
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M P George of the Delhi Pollution Control Committee (DPCC) said that while the detailed analysis was on, preliminary data showed that all stations recorded an overall drop in pollutants from 8 am to 3 pm. Said Anumita Roychowdhury, in charge of the air pollution program at the Centre for Science and Environment: “There was a definite dip in pollutants, and though a dip is seen during the day, it was much sharper today than in the previous two days. But we would like to do a longer analysis before attributing it to emissions.”
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Consider the levels recorded in the three monitoring stations in residential areas under DPCC as compared to that last year:
* Mandir Marg showed the deepest dips across the day. PM 10 levels remained lower than last year through out the day. At 1.25 pm, against 359 last year, this year the PM 10 level was 241. At 5.25 pm, compared to 213 last year, PM 10 level was 147. The PM 2.5 level, which was 322 last year at 10.45 am, fell to 163 today. At 4.45 pm last year from a PM 2.5 of 192, this year, it was just 86 at the same ti9me.
* It was a mixed trend at R K Puram. Compared to PM 10 and 2.5 levels of 718 and 585 (in micrograms per cubic metre) respectively at 9.50 am on January 1, 2015, this year, at 9 am, the same levels were at 683 and 556 respectively. (Permissible level for both is 100 for PM 10 and 60 for PM 2.5).
At 10.50 am, compared to 626 and 394 respectively for the same pollutants last year, this year at 11 am, PM 10 levels stood at a much lower 295 and at 11.30 am, PM 2.5 levels were recorded at 213.
But by 4.50 pm last year PM 10 levels at the same station stood at 484 against 489 this year. At 6.50 pm last year, the station recorded a PM 10 level of 522 against 743 recorded at 6.30 pm this year. For PM 2.5, last year at 4.50 pm, the station recorded a value of 283 while at 5 pm today, PM 2.5 was recorded at 329.
* At Punjabi Bagh, at 1.35 pm last year, PM 10 was recorded at 650 compared to 729 today. At 2.30 pm however, compared to 659 last year, the value stood at 548 today. At 4.30 pm compared to 267 recorded last year, PM 10 was at 211 today. But at 5.30 pm this year, PM 10 stood at 382 compared to 303 last year. For PM 2.5, compared to 135 at 9.30 am, this year the value stood at 314. But it had dipped at 11.40 am — compared to last year’s 404, it stood at 188 today. However, the trend reversed by 5.30 pm when compared to 141 last year, PM 2.5 was at 223.